Muslim says that the time of the white Protestants in America is over

Unfortunately, I think this also means that America's time is over. The United States became a great nation because of its white Protestant population. In other words, we became great because of our lack of diversity. As our nation becomes increasingly non-white and non-Protestant, we will probably become more and more like Africa, Latin America and the less advanced parts of Asia. If diversity is such a good thing for a country then why is China doing so well economically?